Investigation Into Characteristics Of Radial Piston Valve Plate Type Hydrostatic Pump

Radial piston hydrostatic pump has several advantages like high rated working pressure, strong anti pulsation and high ratio of power to weight, which are suit to the need of vehicle hydrostatic transmission system—higher pressure and rotational speed. Nowadays, valve distribution and axis distribution are adopted in the development of radial piston hydrostatic pump, but they have problems like the imbalance radial force which cause they hard to enhance rotational speed. So, both of them are not suit to the trend of development of higher pressure and rotational speed hydrostatic pump. The dissertation introduces valve plate to design radial piston hydrostatic pump, which solved the imbalance radial force problem, and make it easy to enhance the rotational speed. The work could provide fundamental theory for the design of higher pressure, higher speed and larger flow rate radial piston hydrostatic pump.Kinematical analysis, force analysis, instantaneous pressure model of inside piston/cylinder chamber, suction and discharge chamber of valve plate hydrostatic pump are studied in the dissertation. And the change laws of pressure and flow rate are deduced through mathematic calculation. Then causes of pressure and flow rate change are analyzed in the dissertation. The main investigation work focuses on the flowing several aspects:①Kinematical analysis of radial piston pump's key components were studied. Equations of the position, polar distance, velocity and acceleration of the piston were inferred. Then, the effect of varied geometry structures were analyzed by comparing kinematic parameters.②Based on the kinematical analysis, the forces acted on hydrostatic machine parts were analyzed. Force and momentum equations of main parts were deduced on the assumption that the pump remains in a constant angular speed. Then, utilizing two force models to study the contract stress and deformation, piston length remained inside, friction force, contract force between the two friction pairs. During the investigation processing, the traditional hydraulic pressure was replaced by the instantaneous pressure in the piston chamber, which make the calculation result close to the real operating condition.③The theoretical flow-ripple of a radial piston valve plate type hydrostatic pump was studied. Based on the traditional theory, the instantaneous flow ripple formula was deduced. Then, based on the real relative position of the piston and valve plate, the piston chamber participate the discharge or suction processing can be judged. The actual flow ripple equations of a radial piston pump were presented. Flow ripple and flow ripple frequency were acquired by using simulation calculation.④The model of the discharge area of the piston chamber to the discharge port in the valve plate were analyzed. The smallest cross-section areas were computed by analyzing the geometry of tetrahedral structured slot. Then, formulas of the valve plate opening area for each piston port were deduced. Based on these formulas, the relationship between the valve plate opening area and slot structure were created.⑤The model of instantaneous pressure inside the piston/cylinder chamber, suction, and discharge chamber is created. Based on the conservation laws, taking leakage passed through the pairs clearance, and liquid compressibility into consideration, the piston kinematical volume change, the volumetric volume causing by the leakage happened in the clearance of the friction pairs is considered. The instantaneous pressure formulas were created. Then, get the pressure pulsation and flow ripple in all controlled volume by numerical calculation. The relations between pressure pulsation and flow ripple and slot structure were investigated.⑥According to researching and manufacturing of the radial piston pump test system, some references for developing new radial piston valve plate type pump were acquired. FFT analyzing method was adopted to acquire a frequency-domain plot, which shows that there are other distinc frequencies in discharge pressure spectrogram and suction pressure spectrogram besides the piston kinematical frequency. It means that not only the kinematical frequency but also some other factors are the reason to achieve this result. The kinematical frequency depends on the piston's number and rotate speed,ω. The equitation of frequency is f = n·z /60 .